Showing papers in "Molecular Crystals and Liquid Crystals in 1977"
TL;DR: The development and current state of knowledge of ferroelectric liquid crystals are reviewed in this paper, where the Curie point and effects visible in freely suspended films are compared with crystalline ferroelectrics.
Abstract: The development and the current state of knowledge of ferroelectric liquid crystals are reviewed. Symmetry considerations first indicated that a ferroelectric phase should exist. Synthesis of new molecules led to the first experiments on electro-optical properties, indicating a spontaneous polarization. Various studies of bulk samples, including further electro-optical effects, shear induced polarization, pyroelectric effects, and switching experiments are discussed. Studies of the Curie point and effects visible in freely suspended films are summarized. Comparisons with crystalline ferroelectrics are made. Some further work and possible applications are indicated.
361 citations
TL;DR: In this paper, the splay and twist elastic constants of pentyl, hexyl, heptyl and octyl cyanobiphenyls (5CB, 6CB, 7CB and 8CB respectively) have been determined by the Freedericksz transition method.
Abstract: The splay and twist elastic constants (k 11 and k 22) of pentyl, hexyl, heptyl and octyl cyanobiphenyls (5CB, 6CB, 7CB and 8CB respectively) have been determined by the Freedericksz transition method. The results are compared with the bend elastic constants (k 33) and order parameters (S) of these compounds reported by us in an ealier paper, as also with the heats of transition (δH) determined using a differential scanning calorimeter and the temperatures of transitions (T NI). T NI, and k 33 near T NI, exhibit alternation for all the four compounds. On the other hand, S, δH, and k 11 and k 22, near T NI exhibit alternation only for the first three compounds and increase between 7CB and 8CB. It is concluded that (ζ⊥/ζ∥), the ratio of the transverse to the longitudinal correlation lengths of the smectic A type cybotactic order increases between 7CB and 8CB.
165 citations
TL;DR: In this article, experimental evidence is presented indicating that there are two distinctly different kinds of smectic C-to-smectic A transitions: first order with zero tilt and second order with non-zero tilt angle in both phases.
Abstract: Experimental evidence is presented indicating that there are two distinctly different kinds of smectic C to smectic A transitions. The first type is second order with zero tilt in both phases, the second type is first order with a non-zero tilt angle in both phases. The model for the second type of transition is an “uncoupling” of the tilt directions of adjacent layers in the smectic -A phase.
142 citations
TL;DR: In this article, a detailed study on the phase diagram of mixtures containing 4-cyano- 4-n-octyloxybiphenyl and 4-hexyloxy-phenyl-4-nbutyl blenzoate has yielded further insight into the nature of the "solid-like" phase.
Abstract: Non-linear behaviors of nematic-isotropic transition temperatures and the appearance of the “solid-like” phase found in the mixtures between MBBA and 4-cyano-4-n-pentylbiphenyl (CPB)1 are now found to be quite general among many other nematogens. The cyano-group containing nematogens do not have to be biphenyl derivatives, nor do the “donner” type molecules need to be limited to Schiff Bases and azo-type compounds. This type of phase diagram has also been obtained in mixtures of CPB with phenyl benzoates, azoxy and tolan nematogens. Other cyano-group containing nematogens, such as substituted 4′-cyanophenyl benzoates and 4′alkoxybenzylidene-4-aminobenzonitriles gave rise to behavior identical with the above nematogens. A detailed study on the phase diagram of mixtures containing 4-cyano- 4′-n-octyloxybiphenyl and 4′n-hexyloxy-phenyl-4-n-butyl blenzoate has yielded further insight into the nature of the “solid-like” phase. The smectic thermal stability of the alkoxycyanobiphenyl decreased sharply ...
96 citations
TL;DR: In this article, the four classes of 2,5-disubstituted cyano-alkylphenyl- and alkyl-cyanophenyl-pyrimidines have been prepared.
Abstract: The four classes of 2,5-disubstituted cyano-alkylphenyl- and alkyl-cyanophenyl-pyrimidines have been prepared.
83 citations
TL;DR: The static dielectric constants of the following compounds have been measured as functions of temperature in their nematic and isotropic phases: (i) 4′-nalkyl-4-cyanobiphyenyls, (ii) trans-p-n-alkoxy-α-methyl [pacute]-cyanophenyl cinnamates and (iii) CBOOA.
Abstract: The static dielectric constants of the following compounds have been measured as functions of temperature in their nematic and isotropic phases: (i) 4′-n-alkyl-4-cyanobiphyenyls, (ii) trans-p-n-alkoxy-α-methyl [pacute]-cyanophenyl cinnamates and (iii) CBOOA. All these exhibit a very large positive dielectric anisotropy because of the C≡N end group. For all the compounds the average dielectric constant ϵ evaluated from the measured values of ϵ ∥ and ϵ∥ is, throughout the nematic phase, less than the extrapolated isotropic value. Further, ϵ decreases with decreasing temperature, the effect being greter in compounds whose nematic phase is preceded by smectic phase. These facts are in conformity wiht the model of antiferroelectric short range order proposed by Madhusudana and Chandrasekhar. For the two homologous series (i) and (ii), the dielectric anistropy does not show an alternation with increasing chain length, but decreases continuously.
77 citations
TL;DR: In this article, the synthesis of two dithiolato nickel complexes carrying aliphatic substituents was described, and both compounds exhibit mesomorphic properties, and they were shown to have a mesomorphic property.
Abstract: The synthesis of two dithiolato nickel complexes carrying aliphatic substituents is described. Both compounds exhibit mesomorphic properties.
60 citations
TL;DR: In this article, the flow patterns formed by the electrohydrodynamic effect of the nematic liquid crystal were observed and it was found that the phase diagram made from the observation bears a strong resemblance to the phase diagrams made by the authors.
Abstract: The flow patterns formed by the electrohydrodynamic effect of the nematic liquid crystal are observed. It is found that the phase diagram made from the observation bears a strong resemblance to tha...
52 citations
TL;DR: In this article, the dispersion of ϵ∥ in the frequency range of 1-10 MHz has been studied for 4′-n-alkyl-4-cyanobiphenyls (pentyl to octyl) at different temperatures in the nematic phase.
Abstract: The dispersion of ϵ∥ in the frequency range of 1-10 MHz has been studied for 4′-n-alkyl-4-cyanobiphenyls (pentyl to octyl) at different temperatures in teh nematic phase. It is established for the ...
51 citations
TL;DR: Collagen fibrils provide a biological example of smectic A liquid crystals and demonstrate spiralling of their constituent chiral molecules, about the normal to their layers, when they undergo a...
Abstract: Collagen fibrils provide a biological example of smectic A liquid crystals. They demonstrate spiralling of their constituent chiral molecules, about the normal to their layers, when they undergo a ...
50 citations
TL;DR: In this paper, the self diffusion coefficients and the proton relaxation times have been measured in dependence of temperature in a series of p-alkanoyl-benzylidene-P'-aminoazobenzenes.
Abstract: The self diffusion coefficients and the proton relaxation times have been measured in dependence of temperature in a series of p-alkanoyl-benzylidene-P'-aminoazobenzenes. Together with the frequenc...
Abstract: We study the distortion of a chiral smectic C, under a shear applied parallel to the plane of the layers, using an original technique based on the modification of the conoscopic image. Both the amplitude of the distortion and the phase lag between the alternating applied shear and the deformation are found to vary like the flow induced transverse polarization (described in Ref. 7). The behaviour is understood in terms of a viscoelastic-nematic-like model and of a simplified optical description which gives account of the displacement without deformation of the conoscopic image.
TL;DR: In this paper, the capacitance versus voltage (C-V) measurements are used for analyzing electro-optical properties of twisted bematic LCDs, where resulrs are presented in the form of reduced capacitance, and the effective voltage induced distortion of the LC is determined by monitoring CR-V.
Abstract: Magnetocapacitive null (MCN) and capacitance versus voltage (C-V) measurements are valuable tools for analyzing electro-optical properties of twisted bematic LCDs. the C-V technique is particularly useful when resulrs are presented in the form of reduced capacitance CR(V) = [C(V) - C]/(C∥ - C1) = sin2α, where αe(V) is an effective molecular tilt. Thus, the effective voltage induced distortion of the LC is determined by monitoring CR-V.
TL;DR: The C1-C8 and C10 members of the homologous series of terephthal-bis-n-alkylaniline (including TBBA) have been prepared by the condensation of 4-alkylines with terephthaldehyde.
Abstract: The C1-C8 and C10 members of the homologous series of terephthal-bis-n-alkylaniline (including TBBA) have been prepared by the condensation of 4-alkylanilines with terephthaldehyde. Synthesis of the anilines was achieved through a Friedel-Crafts acylation of acetanilide followed by a Wolff-Kishner reduction. Interphase transitions between solid, mesomorphic and isotropic phases were studied by hot-stage microscopy and DTA. The nematic phase was observed in the C1-C7 homologs, the smectic A and C phases in the C3-C10 compounds and the smectic H(B) phase in the C2-C10 homologs. An additional smectic phase with a mosaic texture was observed in the C5 homolog and some unexplained anomalies were found in the phase transition behavior of the C2 and C3 compounds. A study of the textures of the smectic C phases as a function of temperature indicated that all these phases have a temperature dependent tilt angle. Relationships between structure and mesomorphic properties as well as with thermodynamic data ...
TL;DR: In this paper, orientational order is a property of the liquid crystalline phases which has not been well etermined and only that order which is described by the parameter S = = <2/...
Abstract: Although of fundamental interest, orientational order is a property of the liquid crystalline phases which has not been well etermined. Only that order which is described by teh parameter S = = <2/...
TL;DR: In this article, the authors decrivons the technique dilatometrique that nous avons utilisee for etudier le polymorphisme smectique de tous les termes pairs (4 ⩽ n ⩾ 18) of la serie homologue des 4,4′-di(p, n-alcoxybenzylideneamino) biphenyles.
Abstract: Dans cet article, nous decrivons la technique dilatometrique que nous avons utilisee pour etudier le polymorphisme smectique de tous les termes pairs (4 ⩽ n ⩾ 18) de la serie homologue des 4,4′-di(p, n-alcoxybenzylideneamino) biphenyles. Les transitions polymorphiques sont caracteisees par une augmentation rapide du volume dans un intervalle etroit de temperature. Pour chaque terme de la serie, trois phases smectiques sont observees par elevation de temperature. Les temperatures de transition entre ces phases sont determinees. Toutes les transitions entre phases mesomorphes sont reversibles. Seule la transition entre le cristal et la premiere phase smectique ne l'est pas; a temperature decroissante, cette transition presente une forte hysteresis, indiquant la cristallisation des queues paraffiniques des molecules; la cinetique de cette cristallisation est aussi decrite. Les valeurs des volumes molaires sont rapportees en fonction de la temperature. La precision de celles-ci est estimee de l'ordre...
TL;DR: In this article, the effect of terminal substituents on the variation of the nematic-isotropic transition temperature with molecular structure was evaluated with the aid of expressions for TN1 from molecular-statistical theories.
Abstract: In this review some experimental results on the variation of the nematic-isotropic transition temperature TN1 with molecular structure will be evaluated with the aid of expressions for TN1 from molecular-statistical theories. The effect of terminal substituents on TN1 and some typical trends in the values of TN1 for the members of homologous series can be understood from changes in the anisotropic dispersion forces as discussed in Maier and Saupe's theory. The effects of some other structural changes in the molecules on TN1, as for example the variation of central groups, cannot be explained on this basis. Probably it is necessary to take into account as well the molecular repulsions due to the excluded volume.
Journal Article•
TL;DR: In this article, the behavior of a lattice version of the Maier-Saupe model near the clearing point is investigated using a biased Monte Carlo technique, where the lattice model consists of an array of unit vectors, which are located at the sites of a simple-cubic lattice with periodic boundary conditions and interact by way of a nearest neighbour coupling.
Abstract: Abstract The behaviour of a lattice version of the Maier-Saupe model near the clearing point is investigated using a biased Monte Carlo technique. The lattice version consists of an array of unit vectors, which are located at the sites of a n x n x n (n = 14, 16, 18, 20) simple-cubic lattice with periodic boundary conditions and interact by way of a nearest neighbour coupling. The system undergoes a first order phase transition with a spontaneous order S = 0.333 ± 0.009 at the clearing temperature Tc given by βce = 0.894 ± 0.001, where e denotes the maximum interaction energy between two nearest neighbours. The pretransitional light scattering in the isotropic phase can be reasonably well described by [T - Tc∗]−1, with (Tc - Tc= 0.009 ± 0.007 for n = 14 and (Tc - Tc∗)/Tc = 0.007 ± 0.004 for n = 16. This type of divergence is in agreement with experiment.
TL;DR: In this paper, the behavior of a lattice version of the Maier-Saupe model near the clearing point was investigated using a biased Monte Carlo technique, and the results showed that the system undergoes a first order phase transition with a spontaneous order S = 0.333 ± 0.009 at the clearing temperature Tc given by βce.
Abstract: The behaviour of a lattice version of the Maier-Saupe model near the clearing point is investigated using a biased Monte Carlo technique. The lattice version consists of an array of unit vectors, which are located at the sites of a n x n x n (n = 14, 16, 18, 20) simple-cubic lattice with periodic boundary conditions and interact by way of a nearest neighbour coupling. The system undergoes a first order phase transition with a spontaneous order S = 0.333 ± 0.009 at the clearing temperature Tc given by βce = 0.894 ± 0.001, where e denotes the maximum interaction energy between two nearest neighbours. The pretransitional light scattering in the isotropic phase can be reasonably well described by [T - Tc∗]−1, with (Tc - Tc= 0.009 ± 0.007 for n = 14 and (Tc - Tc∗)/Tc = 0.007 ± 0.004 for n = 16. This type of divergence is in agreement with experiment.
TL;DR: In this article, the order parameters of substituted azobenzenes and phenylazothiazole, -benzothiazoles and -heterocyclic compounds dissolved in a nematic liquid crystalline host have been determined.
Abstract: The order parameters (S) of a number of substituted azobenzenes and phenylazothiazole, -benzothiazole and -heterocyclic compounds dissolved in a nematic liquid crystalline host have been determined. The measured order parameters for a class of azo compounds bear a strong relationship to the structure of the dye. For azobenzenes, there is an additivity of substituent effects which leads to good agreement between empirically-derived and observed S values. Disazo dyes give higher S values than the corresponding monoazo dyes. For heterocyclic phenylazo dyes, the end group substituents on the phenyl ring play a significant role in influencing S, whereas the nature of the heterocyclic system, as well as the end group substituents on the heterocyclic ring, are only of minor importance. The presence of an N-H moiety as part of a heterocyclic ring, or the fusion of a benzene ring onto a heterocyclic ring, can lead to significant changes in the order parameter.
TL;DR: In this article, the authors measured the temperature dependence of the apparent viscosity of three liquid crystals: methoxybenzylidene butylaniline (MBBA), hexyloxybenzinitrile amino benzonitrile (HBAB), and cyanobenzylidenes octyloxyaniline(CBOOA) using the Haake-Hoeffler falling ball and Ostwald-Poiseuille viscometers.
Abstract: Using the technique of conventional viscometry (Haake-Hoeffler Falling Ball and Ostwald-Poiseuille viscometers), we have measured the temperature dependence of the apparent viscosity of three liquid crystals: methoxybenzylidene butylaniline (MBBA), hexyloxybenzylidene amino benzonitrile (HBAB) and cyanobenzylidene octyloxyaniline (CBOOA). The measurements with the falling-ball show a small discontinuity in the apparent viscosity of (HBAB) at ∼ 91°C, where the flow properties of this compound have been found to change from one flow regime in which the “classical” molecular alignment with the flow can be observed (T > 91°C) to another regime in which this alignment cannot be observed (T < 91°C). However, in spite of this small discontinuity, the apparent falling-ball viscosity which we measured for (HBAB) is still very close to the Miesowicz viscosity, ηB, obtained by constraining the director n to remain parallel to the velocity vector during the measurements. Measurements performed with the Ostwa...
TL;DR: Seventeen clathrate hydrates of hydrogen and/or fluorine containing molecules have been identified, mostly from the characteristic nuclear magnetic resonance line shapes observed when the hyddrates are prepared from D2O.
Abstract: Seventeen new clathrate hydrates of hydrogen and/or fluorine containing molecules have been identified, mostly from the characteristic nuclear magnetic resonance line shapes observed when the hydrates are prepared from D2O.
TL;DR: The Maier-Saupe theory of nematic liquid crystals as discussed by the authors uses a one-body mean field potential of the form φ2 nP2(cos θ), where θ is the angle between the molecular long axis and the nematic directo...
Abstract: The Maier-Saupe theory of nematic liquid crystals, which uses a one-body mean field potential of the form φ2 nP2(cos θ), where θ is the angle between the molecular long axis and the nematic directo...
TL;DR: In this article, the surface tension of CBOOA has been investigated in its smectic A, nematic and isotropic phases. And the results show that surface tension-temperature (γ-T) shows a positive slope throughout the A-nematic phase, changes sign at the smectics A-Nematic transition, remains negative over the entire nematic range and again reverses sign immediately after the nematic-isotropic transition, the positive slope now continuing for a few degrees in the isotropics phase.
Abstract: In continuation of our previously reported experimental studies on the surface tension of liquid crystals, measurements have been carried out on p-cyanobenzylidene p'-n-octyloxyaniline (CBOOA) in its smectic A, nematic and isotropic phases. The surface tension-temperature (γ-T) characteristic shows a positive slope throughout the smectic phase, changes sign at the smectic A-nematic transition, remains negative over the entire nematic range and again reverses sign immediately after the nematic-isotropic transition, the positive slope now continuing for a few degrees in the isotropic phase. These trends are compared with the theoretical predictions of Croxton and Chandrasekhar.
TL;DR: The carbonaceous mesophase as mentioned in this paper is a lamellar liquid crystal in which space is filled by plate-like molecules which may vary in size and shape but tend to pack in parallel arrays.
Abstract: When the organic precursors to coke and manufactured graphite (petroleum and coal-tar pitches) are carbonized, large, flat, polynuclear aromatic molecules are formed by the reactions of aromatic polymerization. As the molecular weights approach 1500, usually near 450 C, the molecules condense to form a liquid crystal which has been termed the carbonaceous mesophase. The distinctive feature of the carbonaceous mesophase is the plate-like molecule, in contrast to the rod-like molecule of nematic liquid crystals. The carbonaceous mesophase thus appears to be a lamellar liquid crystal in which space is filled by plate-like molecules which may vary in size and shape but tend to pack in parallel arrays. These arrays are free to bend and twist as they trace out a lamelliform or Mobius morphology with topological discontinuities which bear similarities to the disclination structures found in conventional liquid crystals. Two types of lamellar disclinations may be conceived: layer-stacking disclinations r...
TL;DR: The comparison between experimental condition in two experiments measuring MBBA bend flexo-coefficient and an analogy with lyotropic liquid crystals lead to the concept that the reason for the big....
Abstract: The comparison between experimental condition in two experiments measuring MBBA bend flexo-coefficient and an analogy with lyotropic liquid crystals lead to the concept that the reason for the big ...
TL;DR: Two homologous series of liquid crystalline Schif base esters of the following structural formula are synthesized by condensing p)p′ -n-alkoxybenzoyloxy)benzaldehydes with p-anisidine and p-toluidine as mentioned in this paper.
Abstract: Two homologous series of liquid crystalline Schif base esters of the following structural formula are synthesized by condensing p)p′ -n-alkoxybenzoyloxy)benzaldehydes with p-anisidine and p-toluidine.
TL;DR: In this paper, the authors have clarified some dyes available for the guest-host cell and the influence of the thickness of the liquid crystal layer in a cell on color switching and response characteristics have been made clear.
Abstract: The liquid crystal display devices using the guest-host interactions do not require that substrates are optically flat, and have wide viewing angle. Therefore, the authors have studied the dichoric dyes used in these display devices. A part of the results obtained was described in another journal. In this paper, the authors have clarified some dyes available for the guest-host cell. The influence of the thickness of the liquid crystal layer in a cell on color switching and response characteristics have been made clear. If the product of the dye concentration and the cell thick ness is kept constant, the variation of the cell thickness will not change the color switching characteristics. The recovery time is proportional to the square of the cell thickness. By adjusting the dye concentration we can make a thin cell with a good color switching characteristic and with the short recovery time.
TL;DR: In this article, the volume changes associated with the liquid crystal phase transitions in n-p-cyanobenzylidene-p -octyloxyaniline (CBOOA) were measured using a differential dilatometer technique, and the critical exponent derived from this data is consistent with the mean field theory of the isotropic phase.
Abstract: Using a differential dilatometer technique, we have measured the volume changes associated with the liquid crystal phase transitions in n-p-cyanobenzylidene-p-octyloxyaniline (CBOOA). A volume discontinuity is not observed at the smectic A to nematic transition, and we conclude that it is less than 10−5 ml/g. The volume behavior in a range ± 15[ddot]C about the nematic-isotropic transition has been studied. The critical exponent derived from this data is consistent with the mean field theory of the isotropic phase.
TL;DR: In this article, the 4-n-alkylphenyl 3-cyano-or 3-fluoro-4-nalkoxybenzoates and the 4-(3-cyano)-phenyl 4-bromo-4 n-alkoxy-or 4 nalkylbenzoyloxy-)benzoate derivatives were prepared.
Abstract: Thirty four benzoate derivatives were prepared. They belong to the two following series: the 4-n-alkylphenyl 3-cyano-or 3-fluoro-4-n-alkoxybenzoates and the 4-n-alkylphenyl 4-(3-cyano-or 3-bromo-4-n-alkoxy-or 4-n-alkylbenzoyloxy-)benzoates. In the latter series all the compounds are measomorphic; in the former one, only 3-cyano compounds with long alkoxy chain, exhibit a small mesomorphic range. All the cya[ngrave]o compouns exhibit very high negative dielectric anisotropies.